1. Field of the Invention
The present invention relates to a furnace wall construction for industrial use, and particularly to a multi-layered furnace wall construction comprising an innermost layer made of blocks of refractory fibers.
2. Prior Art
In the conventional furnaces of industrial uses, for example heating and forging furnaces used in the steel-making industry or heating furnaces for general purposes used in other fields of art, the internal surface of the furnace wall is covered with refractory fibers, such as ceramic fibers, to improve the heat insulating function of the furnace wall. In the process for covering the inner wall surface of an industrial furnace, it is a common practice to use refractory fiber blocks which are secured over the surface of the furnace wall made of a non-fibrous material, such as plastics refractories, using a refractory mortar as the adhesive. Although the refractory fiber blocks may be easily applied on the wall of the furnace, this known practice is unsatisfactory for the reason that the refractory fiber blocks are not reliably secured on the wall but are susceptible to separation from the wall. Particularly, when the refractory fiber blocks are cemented on the ceiling of a furnace using a refractory mortar as the adhesive, almost all fiber blocks are separated and fall down from the ceiling within one or two months. Thus, this known practice is far from the one which can be recommended as a reliable and satisfactory manner for applying the refractory fiber blocks on the furnace wall.
A multi-layered furnace wall construction is known, wherein a plurality of stud bolts made of a metal, such as stainless steel or steel, is secured to an iron shell forming the outer contour of a furnace, with the ends of the stud bolts extending inward of the furnace through a rock wool layer applied on the inner surface of the iron shell and a ceramic fiber layer superimposed on the inner side of the rock wool layer, and the ceramic fiber layer is fastened by metal washers fixed to the free ends of respective stud bolts. However, this known furnace wall construction is not suited for constructing a furnace which is exposed to a relatively high temperature, because the furnace wall of this type is not durable under a high temperature condition due to shrinkage of ceramic fibers and oxidation of stud bolts and washers made of a metal. It has been proposed to improve the furnace wall construction of this type by further providing, inward of the aforementioned ceramic fiber layer, a layer of crystallized aluminous fibers (felt form) which withstand a higher temperature environment and by substituting stud bolts and washers of ceramic composition for the metallic stud bolts and washers. However, the improved furnace wall construction in accordance with the former-made proposal has a disadvantage that the crystallized aluminous fiber layer (felt) is cracked due to shrinkage to fall down from the wall when the furnace temperature is raised higher. Moreover, in all of the known furnace wall constructions described above, ceramic fibers and/or crystallized aluminous fibers are oriented generally in the direction parallel to the surface plane of the furnace wall (the lining of this type will be referred to as layer lining). When the layer lining is exposed to hot combustion air flow blown from a burner or the like, the fibers at the surface portion of the lining are peeled off, the peeling occurring along the parallel orientation direction, so that the lining layer becomes thinner to result in loosening of the fastening force applied by the stud bolts, leading to fall-down of a mass of fiber block. Furthermore, development of cracking causes immediate draggling or partial separation of the lining layer.
In a further known furnace wall construction, a plurality of L-shaped studs made of a metal, such as stainless steel or steel, is secured to an iron shell forming the outer contour of a furnace, with the L-shaped free ends of the studs extending inward of the furnace for piercing corresponding fibrous refractory blocks in which fibers constituting the refractory blocks are oriented in the direction perpendicular to the surface plane of the furnace wall (the lining of this type will be referred to as stack lining). In this stack lining construction, a plurality of fibrous refractory blocks is stacked inside of the iron shell while allowing the fibers constituting the fibrous refractory blocks to extend perpendicular to the surface plane of the iron shell wall, the one end face of each fibrous refractory block engaging with the inside surface of the iron shell and the other end face of the block forming free end constituting the inner wall surface of the furnace. With this construction, even when crackings are caused by shrinkage at some portions of the innermost surface of the lining under the influence of heating, immediate separation of the lining block carried by the L-shaped studs does not occur. However, in the known stack lining construction, since the fibrous refractory blocks must be arranged such that the fibers contained in each refractory are oriented in the direction perpendicular to the surface plane of the iron shell, the entire mass of the lining from the innermost surface thereof to the low temperature portion engaging with the inside face of the iron shell must be made of crystallized aluminous fibers which withstand a higher temperature environment. Such a construction is uneconomical, because the crystallized aluminous fiber material is expensive.